Knot detecting and rejecting attachments for unifil-type bobbin winding machines

ABSTRACT

A bobbin-winding machine for automatic bobbin change looms of the &#39;&#39;&#39;&#39;Unifil&#39;&#39;&#39;&#39; type winds bobbins from a series of yarn packages, the end of one package being tied to the beginning of another so that winding continues without interruption. Wound bobbins are doffed when full by a doffing cycle, which stops winding, transfers the wound bobbin through a guide track into a magazine, cuts threads, and at the end of the cycle restarts winding. Knots are avoided by passing the yarn through an opening, such as a slot, large enough to pass yarn but smaller than a knot, so that when a knot passes the plate having the opening trips actuating switches to start a doffing cycle even through a bobbin is not completely wound and includes tilting of the guide track so that bobbins containing knots are fed into a separate magazine, from which they can be removed by hand, the knot cut off, and the bobbin introduced into the main magazine with the other wound bobbins. The end of the doffing cycle actuates the switches and resets the trip plate with its opening for yarn.

United States Patent [72] inventors AlbertJosephRlchards;

Henry Eugene Gaillardetz, both of Lowell, Mass.

[21] AppLNo. 21,087

[22] Filed Mar. 19.1970

[45] Patented Aug. 10, 1971 [73] Assignee J.P.Stevens&Co.,lnc.

New York, NX.

[54] KNOT DETECTING AND REJECTING ATTACHMENTS FOR UNlFIL-TYPE BOBBIN 2,780,418 2/1957 Davis 3,291,160 12/1966 Veneyetal i.

ABSTRACT: A bobbin-winding machine for automatic bobbin change looms of the Unifil" type winds bobbins from a series of yarn packages, the end of one package being tied to the beginning of another so that winding continues without interruption. Wound bobbins are doffed when full by a doffing cycle, which stops winding, transfers the wound bobbin through a guide track into a magazine, cuts threads, and at the end of the cycle restarts winding. Knots are avoided by passing the yarn through an opening, such as a slot, large enough to pass yarn but smaller than a knot, so that when a knot passes the plate having the opening trips actuating switches to start a doffing cycle even through a bobbin is not completely wound and includes tilting of the guide track so that bobbins containing knots are fed into a separate magazine, from which they can be removed by hand, the knot cut off, and the bobbin introduced into the main magazine with the other wound bobbins. The end of the doffing cycle actuates the switches and resets the trip plate with its opening for yarn.

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' snmanrs INVEN'I'ORS. ALBERT JOSEPH R/CHARDS HENRY EUGENE GA/LLARDET- ATTORNEY KNOT DETECTING AND REJECTING ATTACHMENTS FOR UNIFlL-TYPE BOBBIN WINDING MACHINES BACKGROUND OF THE INVENTION One of the developments introduced into looms many years ago was an automatic exchange of a bobbin or quill in the shuttle which was practically empty for a full-wound bobbin. The exchange was automatically carried out without stopping the loom and occurred at the brief instant at the end of a shut tle motion when it is substantially stationary. A magazine with full bobbins was located in proper position for the exchange of bobbins. In earlier machines these magazines were charged with full bobbins from time to time by hand. The manual filling of the magazine was a drawback as it required addi tional labor. As a result, more than a decade ago an attachment for looms with bobbin exchanges in the shuttle was put on the market by the Leesona Company under their trade name Unifil. This attachment was bolted onto looms and automatically wound bobbins from large pirns or thread packages the yarn being guided by a yarn guide along the axis of the bobbin as it was wound. When a bobbin is fully wound, the yarn guide strikes the sizing plate which releases the sizing finger which stops winding and starts a doffing cycle. This transfers full bobbins through a guide track into the magazine for changing bobbins in shuttles on the loom. At the end of the doffing cycle the yarn or thread is cut and the yarn guide restored to its initial position which releases the sizing plate. If the magazine was not full, this was sensed and another winding cycle started. followed in turn by another doffing cycle. In order to assure that there were always full bobbins available for changing in the shuttles, the bobbin winding machine wound at a somewhat higher rate than the loom used the wound bobbins, so that the magazine was always maintained sufficiently full so that there were wound bobbins available for change and the loom never had to shut down.

Because of the very high speed of bobbin winding, which often approximated 8,000 r.p.m., yarn or thread was rapidly consumed, and even a large package would ordinarily last for a comparatively short time, for example 20 minutes. In order to assure that the winding machine always had plenty of yarn, it was provided with mountings for a plurality of yarn packages, for example two to four. The yarn from the end of one package was tied to the yarn from the beginning of the next package and so continuous winding was maintained. Of course with a number of packages, when the yarn was coming either from the last package or one before, fresh packages were mounted by the weaver and, of course, had the beginning of their thread tied to the end of the thread of the preceding package Since mounting new packages occurred only at longer intervals, the weaver or machine operator had plenty of time and no additional labor was required, as was formerly necessary for loading wound bobbins into the magazine.

The Unifil type of bobbin winder achieved enormous commercial success and is an attachment which is widely used on most looms or other fabric-forming machines in which bobbins are to be exchanged when they become empty without stopping the machine.

Great as the success of the Unifil-type bobbin winder has been there was one drawback. The knots which tied the thread from the end of one package to the start of the other were wound onto the bobbins and except for a rare coincidence did not come exactly at the end of a bobbin but occurred at any point in the bobbin where the knot happened to reach it. Because of the high speed of winding, it could not be noticed that a particular bobbin contained a knot, and so when such a bobbin was automatically introduced into a shuttle the knot was woven into the fabric. With some fabrics of rough texture this was not serious, but in other fabrics it constituted a defect. However, this was tolerated in order to enjoy the great advantages of the high speed winding of bobbins. In the standard Unifil"-type of bobbin winder, empty bobbins discharged from a shuttle were collected and returned to the winding machine in a magazine for empty bobbins which were introduced at the end of each doffing cycle.

SUMMARY OF THE INVENTION 7 The drawback presented by knots is completely solved by the present invention, which may be considered as an improvement on the bobbin-winding machines or attachments of the Unifil"-type. Winding, doffing cycle and full-bobbin magazines are not changed by the present invention, nor is the supply from a number of packages with yarn at the end of one package tied to the yarn at the beginning of the next one.

However, in the present invention this yarn passes through an opening, usually a jaw slot in a trippable plate, the dimensions of the slot and the tripping force needed were chosen so that a particular yarn would pass through without sufficient friction to trip the plate. However, when a knot comes, this trips the plate down, the knot slides off, and there is no excessive force on the yarn.

When the plate trips, it throws an electric switch which also throws another switch and through solenoids bringing about the following sequence of operations. One switch or relay with the solenoid initiates a doffing cycle, which would otherwise only be initiated when a bobbin is fully wound and its sizing plate starting a dofting cycle. The doffing cycle is started before a bobbin is fully wound and operates in the normal manner with one exception, which will be described. There is provided a tray or a magazine to receive bobbins which have a knot wound in. This tray or magazine is mounted at an angle to the main magazine which receives wound bobbins in the ordinary operation of the bobbin-winding mechanism. The modification in the doffmg cycle which is initiated by the passage of a knot rather than by the complete winding of a bobbin also actuates through a second switch and solenoid a linkage which tips the guide track so that the partially wound bobbin cannot fall into the regular magazine but rolls down the outside of the tipped track into the reject tray or bin.

At the end of the knot-actuated doffing cycle both solenoids release allowing the guide track to return to its normal position so that the next fully wound bobbin will drop down the guide track into the main magazine, and releasing the sensor allowing the winder to start and operate normally. At the end of the knot-actuated doffmg cycle the knot-tripping plate is reset through linkages, so that it is ready to be tripped when the next knot comes along.

The knot-tripping plate and associated switches for a long time present some problems, two of which at times were fairly serious. With modified bobbin winders on some looms operation of the knot-actuated special doffing cycle proceeded for many months or even more than a year, but when a bobbin winder was mounted on another loom there was malfunctioning. Finally, the cause was found in the nature of the switch controlled by the tripping plate and a second switch which controlled the guide track tipping when a knot-actuated doffmg cycle started. For a long time mercury switches were used, but it finally became apparent that the reason why some looms worked satisfactorily and not others lay in the different degrees of vibration of the looms. With looms that had very high vibration, mercury switches could be actuated even through no knot was passing through. Once these switches were replaced with switches which are not vibration sensitive and which have solid contacts, the problemceased, and regardless of what loom was being operated reliable operation proceeded month after month.

A second problem arose with certain yarns, such as certain covered elastic yarns. Even though a trip plate with an opening of the proper size was used, some of these yarns presented sufficient friction so that the plate would be tripped when no knot was passing through. This required adjusting the amount of force required to trip the plate and was eventually taken care of by a change in the position of the pivots about which the plate pivoted and its linkages. When these were adjusted to require an adequate amount of force in order to cause the plate to trip, no problems arose and the adjustment, though not critical. was sufficiently sensitive so that continuously reliable tripping withknots resulted, but without so great force a that would break the yarn.

Y The present'invention is useful with a very wide range of yarns, including elastic yarns, covered or uncovered; and extremes in. yarn cross section required tripping plates with somewhat different-sized openings or jaws. As the plates are readily exchangeable, it takes but a few moments to change tripping plates when there is a very different size or characwould be possible to operate for a long time with yarns of a particular size range without changing plates.

The need for fairly careful adjustment of tripping forces and plate-size openings is particularly noticeable with elastic yarns, such as'covered elastic yarns, where it is difficult to v maintain'the yam'diameter in as close tolerances as with some nonelastic yarns. For the more difficult yarns a replaceable trip platewith orifice size and force required for tripping that is right for a particular class ofryarns is more important. The

adjustment of tripping force'requir'ed is not critical, although it ,must be taken into consideration. In general somewhat larger yarn op'enings'and somewhat higher tripping forces are normally preferable because the difference between the tripping forceexerted by a knot'and that which is sufficient to break the yarn in most cases is of a different order of magnitude.

When one or more incompletely wound bobbins because of knot-actuated doffingcycles accumulate in the reject tray or magazine. they'can be removed by the operator. a short piece of the end of the yarn pulled out and cut just before the knot is reached, These partially filled bobbins can then be placed in the regular magazine by hand, and sotheyarn usedin winding them is not wasted. The amount of labor required is very small I because a partially wound bobbin is only encountered at con- 1 siderable longerintervals than those required in the exchange of a full bobbin for an empty bobbin in the loom shuttle, and so additional labor'is not required. It should be noted that when-a partially wound bobbin is placed in the magazine it is exchanged in the shuttle in exactly the same manner as a fully wound. bobbin, but of course it does not last'as long and so the exchange mechanism is called into operation sooner, but this presents no problem as the loom is never stopped and it is a matter of complete indifference whether bobbin changes are occasionally more often than in normal operation. In every case the change is initiated by the bobbin becoming practically empty in a shuttle and this is just as reliable with a partially wound bobbin as with one that is fully wound.

It will be noted that the advantages of complete elimination of yarn knot defects are obtained without any offsetting disadvantages. The bobbins are wound reliably and when no knot is present are would fully. just as always, and so the advantages of the present invention do not involve any compromise in any other respects. All that is needed is rudimentary care in changing a replaceable trip plate when there is so great a change in yarn size or characteristic or such plate wear that this becomes necessary. A change takes but a minute or two and requires only a moderate amount of common sense. Fast looms with automatic changes are not devices that are intended to be operated by incompetent people and anyone that is competent to operate the loorn is more than competent to determine whether a change of replaceable trip plate is needed.

It will appear from the discussion above that many elastic yarns require more care than those that are not elastic, and therefore the present invention is particularly useful with bobbin-windingmachines on looms or other fabric-forming equipment which are to produce elastic fabrics and this field is, therefore, of particular importance for the present invention.

BRIEF DESCRIPTION .OF THE DRAWINGS FIG. I is a front elevation with no. knot the yarn;

FIG. 2 is a detail of aportion of the back of the machine;.

FIG. 3 is a front elevation similar to FIG. 1 but with the tripping platetripped by a knot in the yarn;

FIG. 4 is a detail of the rear of the machine when the tripping plate has been tripped as shown in FIG. 3;

FIG. 5 is a top view of the tripping plate, and

FIG. 6 an end view of ,a switch shown inFIGS. 2 and 4 DESCRIPTION OF THE PREFERRED EMBODIMENTS In describing the drawings it should be noted that only so much of a bobbin-winding machine is shown as is necessary tov understand where the knot-preventing mechanism of. the present invention is, attached. Many of the portions of the bob.-

. bin-winding machine'which are not changed, such as thefullbrackets 4 and 5, the former supporting magazines for partiaily or'fully wound bobbins and the latter yarn-tensioning means, shown more or less diagrammatically, at 6 with tension pulleys 7' and the knot-detecting system of the present invention, which will be described below. Yam 8 unwinds from two packages 9 and 10, which are supported on the conventional yarn package holders ll of the bobbin-winding machine. The end 12 of the yarn from one package is tied to the beginning 13 of the second package with a knot l4.-This part of the'bobbin-winding machine is not changed by the present invention.

FIG. 3 shows the beginning of yarn 8 being unwound from the package 9 and illustrates a knot 15 which tied the beginning of the yarn from package 9 to thetailof-the yarn from the preceding package, which is now shown as replaced by new package 10, and of course with the knot 14 to the end 12 of the yarn in package 9. While FIG. 1 shows 'a situationa few moments later after the knot 15 has been eliminated, the description of the operation is clearerif we consider FIG. 1 first. The yarn 8, without any knot in it,- passes over a guide bar or roller 16, and down 1 through the knot eliminating mechanism of the present invention. The yarn extends on down through the traversing yarn guide 17 on a carriage 18 moved by the conventional cam, which is not changed by the present invention and which does not show on FIGS. 1 and 3.

The rapidly rotating spindle 19 is turned by the gearbox 3 and carries the bobbin 20, which is rapidly wound at speeds up to 8,000 rpm. The bobbin is wound, and FIGS. 1 and 3 show it at a point where the winding is about one-third through, until the bobbin is full, at which point in normal operation a doffing cycle is initiated. The initiating mechanism is actuated by the movement the sizing plate which is described below in connection with a knot-actuated doffing cycle. This initiation, I

is part of the conventional bobbin-winding machine and is not described in detail.

The normal doffing cycle includes the following operations: The winding spindle stops, the full bobbin is doffed, passing down through the bobbin guide or track 21 in the usual manner. The track guides the bobbin down into a magazine for full bobbins, which does not show on the drawings as it is obscured by the tray 22 for bobbins which have been partially wound until a knot was reached. The full bobbin has the end of its yarn cut by a conventional mechanism, (not shown), leaving a tail of yarn in suitable position for automatic bobbin exchange in the loom. This mechanism, which is also not changed by the present invention, is not shown in order not to obscure the portions of the winder which constitute the present invention. The next step in the doffing cycle is to drop an empty bobbin 23 from the empty bobbin magazine 24 and to connect it to the spindle 19. This mechanism is also not changed by the present invention and so is not shown for the sake of clarity. Also, only a single empty bobbin 23 is shown in the magazine, though in normal operation there will be several. This ends the doffing cycle, the sizing plate 48 returns to operating position, the spindle 19 starts turning again, and a new bobbin is wound as described above.

Most of the mechanism which has just been described is a standard mechanism of the conventional bobbin-winding machine of the Unifil-type. The shape of the full bobbin guide trade 21 is also the same; but whereas in the conventional winder this track is fixed, in the present invention, as shown in FIG. 1 and 3, the track is pivoted on a shaft 25 attached to a linkage bar 26, which in turn is fastened to linkage bar 42. The operation of this linkage will be described below. Portions of an empty bobbin return mechanism are also shown in FIGS. 1 and 3, although this is unchanged by the present invention. This includes a belt 28 which comes up from the conventional empty bobbin stripper, (not shown). The belt carries a magnet, which is also not shown, that picks up an empty bobbin, carries it up and around the pulley 29 and deposits it into the chute 30 from which it drops into the empty bobbin magazine 24. This operation is, of course, also not changed by the present invention and the showing is, therefore, essentially diagrammatic.

The knot-actuated mechanism of the present invention will now be described. This is mounted on the bracket 5, as shown in FIGS. 1 and 3 and consists of a frame 31 on which there is mounted a normally open switch 32 of a standard type with solid contacts and not being vibration sensitive. The same framework also carries a guide bracket 33 to guide the yarn 8 through an opening 34 in the form ofajaw in a trippable plate 35, the shape of which opening is shown more clearly in the plan view of FIG. 5. The trippable plate has an extension 36 pivoting around a shaft 37. The end of the trippable plate 35, which is slightly bent, contacts a spring-actuated lever 39, which in turn operates the switch 32. In the position in FIG. 1 in which the trippable plate 35 is level, this lever 39 is held in the closed position, which in turn maintains the switch 32 open.

FIG. 3 shows what happens when a knot in the yarn approaches the plate 35. As the knot cannot pass through the jaw 34, the plate is tripped and the knot 15 slides off its end. This pulls the yarn around the guide bar 40 so that as soon as the knot has slipped off the plate 35 the yarn is pulled again into the jaw. In normal operation, as in FIG. 1, the yarn does not touch the bar 40.

Closing of the switch 32 by the movement of the lever 39 initiates the same type of normal doffing cycle even though the bobbin is not full. FIG. 3 shows it about a third full, but of course the knot may arrive at any point in the winding of the bobbin. Because of the very high rate of speed of winding, from 5,000 to as much as 8,000 rpm, there is considerable momentum, and this is sufficient to continue the winding for long enough so that the knot 15 passes through the traversing guide 17 and winds onto the bobbin together with a small tail. This is shown in the bobbin in the tray or magazine 22 at the bottom of FIG. 3. The doffing cycle doffs the bobbin from the spindle even though it is not fully wound and cuts the tail of yarn just beyond the knot in the same manner as if this had been an unknotted stretch of yarn at the end of a fully wound bobbin.

Closing of the switch 32 actuates solenoid 43 on back of machine, and pulls up its plunger as shown in FIG. 4. It pulls up rod 44 which hooks into a linkage and a pivoted member 47. The result is as shown in FIG. 4 that member 47 moves the sizing plate 48 to the left against the pull of the spring 49. The movement of the sizing plate 48 stops the winder and starts the doffing cycle. Also as rod 44 is pulled up it causes a lever 45 to close switch 54 through the lever 27. This actuates solenoid 41 on front of machine and, through linkage 42 and 26 tilts the guide track 21 to the position shown in FIG. 3. As a result the bobbin which is only partially wound with a knot rolls into the tray 22 and does not fall through the track into normal full bobbin magazine as is the case in the untilted position shown in FIG. 1.

It will be noted that in its tilted position the plate 35 permits the lever 39 to remain in the position shown in FIG. 3 and therefore the switch 32 remains closed and correspondingly the solenoids 43 and 41 remain activated.

During the doffing cycle, the conventional grip arm (not shown) moves lever 51, (FIG. 2). This raises rod 52 and as can be seen in FIG. 1, the motion of this rod through a linkage 56 tips up the plate 35 to the normal position. This resets lever 39 opening the switch 32 and all electrical connections for the knot rejection cycle are broken. Deactivation of the solenoid 43 permits the spring 49 to return the sizing plate 48 to normal operating position as shown in FIG. 2.

In the meantime the end of the doffing cycle initiated by the passage of knot causes rod 52 to move down to the position shown in FIG. 3 and the linkage 56 is now moved out of contact with the end of plate 35, so that when the next knot comes through it, the plate can move. The end ofthe doffing cycle, of course, also resumes winding on the empty bobbin which, as in the normal doffing cycle, has been mounted on the spindle l9 and the latter starts turning, initiating another winding cycle. The opening of the switch 32 also deenergizes the solenoid 41 and the weight of the linkage restores the bobbin guide 21 to its normal upright position, which is shown in FIG. 1. From now on the winding proceeds in the normal manner, doffing being initiated only when a bobbin is wound full. Of course the guide 17 is traversed back to its starting position, which occurs at the end of every doffing cycle. Normal winding then proceeds until another knot is encountered, at which point the knot-actuated premature doffing cycle is repeated, as has been described above.

Since a knot is only encountered after a full supply package has been exhausted, which will normally be 20 minutes or more, there is plenty of time for the loom operator to place a second package on its holder, tie its beginning yarn to the end yarn of the other package, and also leaves plenty of time for an operator to remove manually a partially wound bobbin from the tray 22, cut off the yarn just back of the knot and place the partially wound bobbin in the full bobbin magazine of the winder. It will be noted that in due course, when the loom calls for more bobbins, it will receive the partially wound bobbin resulting from the knot-actuated doffing cycle. This, however, does no harm because, as has been mentioned above, even though this partially filled bobbin may last for a much shorter time before it has to be replaced in the loom shuttle, this replacement results from the bobbin being practically empty and of course it makes no difference whether the replacement occurs after a shorter time than that corresponding to a fully wound bobbin.

FIG. 3 illustrates another detail in that it shows a partially wound bobbin with knot passing down through the tray 22 in three different positions. This does not means that there were necessarily three partially wound bobbins in the tray at the same time. The bobbin at the bottom of the tray is positioned so that it can be removed through the tray opening at the bottom readily. Of course if an operator does not remove it before the next partially wound bobbin has gone through the knot-actuated doffing cycle, no harm is done because the tray is large enough to carry more than one partially wound bobbin at a time.

As the tray 22 extends out considerably, there is a little risk that it might pull the thread at too much of an angle so that it would not start winding reliably, and so a wire 57 is provided to hold in the thread sufficiently so that a new winding cycle can be initiated. This wire or guide 57 is not present in a standard bobbin winder and is one of the elements added by the present invention.

We claim:

1. In a bobbin-winding machine for fabric-forming machines having automatic bobbin change when a bobbin has -cle, the winding machine having means for receiving a plurality of yarn or thread packages which have their end yarns tied [u iiir lwginning yams nfiiir'. next succeeding package, the im' movement which comprises, in combination,

a, a trippable trip plate having an opening positioned so that yarn wound onto bobbins passes therethrough, the opening being of dimensions such that yarn passes through without tripping the plate but knots cannot pass through, and trip the plate.

the trippable plate including a pivot on the plate and a tripping force much less than the breaking strength of the yarn and less than the force exerted by a knot,

c. means actuated by the pivoted tripping plate for actuating a switch with solid contacts and insensitive to vibration,

. a plurality of solenoids actuated by the switch, one solenoid initiating a doffing cycle even though a bobbin being wound is not completely wound and a second solenoid tilting the guide means to a position whereby a bobbin in the doffing cycle cannot pass into the magazine but is deflected to one side,

e. a knot-containing bobbin receiving container positioned so that when a bobbin is doffed in the cycle induced by the switch it is conducted to the container, and

f. means actuated by the end of the doffing cycle for restoring the tripping plate into position and resetting the switch, whereby bobbin winding proceeds with normally actuated doffing cycles at the time of a fully wound bobbin so long as there is no knot in the yarn and a knotwound bobbin doffing cycle is only initiated when a knot in the yarn passes through the tripping plate.

2. A device according to claim 1 in which the means actuated by the end of the doffing cycle for restoring the tripping plate into position comprises pivoted linkages and the tripping plate resets the switch and locks it until the tripping plate is actuated by another knot in the yarn.

3. A device according to claim 2 in which the tripping plate is replaceable to provide openings of size suitable for different thicknesses of yarn.

4. A device according to claim 1 in which the tripping plate is replaceable to provide openings of size suitable for different thicknesses of yarn. 

1. In a bobbin-winding machine for fabric-forming machines having automatic bobbin change when a bobbin has become exhausted and which machine includes a full bobbin magazine, bobbin-winding means, a guide track to the magazine for full bobbins, doffing cycle means initiated by sensing means which determine that a bobbin is fully wound, which doffing cycle includes stopping winding, doffing the wound bobbin, cutting the yarn end, and causing it to fall through the guide track into the magazine, means for introducing an empty bobbin and means for returning the winding mechanism to initial position at the end of the doffing cycle, the winding machine having means for receiving a plurality of yarn or thread packages which have their end yarns tied to the beginning yarns of the next succeeding package, the improvement which comprises, in combination, a. a trippable trip plate having an opening positioned so that yarn wound onto bobbins passes therethrough, the opening being of dimensions such that yarn passes through without tripping the plate but knots cannot pass through, and trip the plate, b. the trippable plate including a pivot on the plate and a trippiNg force much less than the breaking strength of the yarn and less than the force exerted by a knot, c. means actuated by the pivoted tripping plate for actuating a switch with solid contacts and insensitive to vibration, d. a plurality of solenoids actuated by the switch, one solenoid initiating a doffing cycle even though a bobbin being wound is not completely wound and a second solenoid tilting the guide means to a position whereby a bobbin in the doffing cycle cannot pass into the magazine but is deflected to one side, e. a knot-containing bobbin receiving container positioned so that when a bobbin is doffed in the cycle induced by the switch it is conducted to the container, and f. means actuated by the end of the doffing cycle for restoring the tripping plate into position and resetting the switch, whereby bobbin winding proceeds with normally actuated doffing cycles at the time of a fully wound bobbin so long as there is no knot in the yarn and a knot-wound bobbin doffing cycle is only initiated when a knot in the yarn passes through the tripping plate.
 2. A device according to claim 1 in which the means actuated by the end of the doffing cycle for restoring the tripping plate into position comprises pivoted linkages and the tripping plate resets the switch and locks it until the tripping plate is actuated by another knot in the yarn.
 3. A device according to claim 2 in which the tripping plate is replaceable to provide openings of size suitable for different thicknesses of yarn.
 4. A device according to claim 1 in which the tripping plate is replaceable to provide openings of size suitable for different thicknesses of yarn. 